We plan to continue in the purification and structural characterization of stage specific subtypes of the histones of sea urchin embryos. We will also take up the question of whether early subtypes become segregated in a subset of cells in the embryo. These studies will involve 1) isolaton of each subtype in pure form; 2) determination of the chemical nature of the differences between them by peptide mapping and sequence analysis; 3) preparation of subtype-specific immune sera; 4) study of locations of the subtypes in the embryo of immunofluorescence.